Generally described, gas turbine engines include a compressor for compressing incoming air, a combustor for mixing fuel with the compressed air and to ignite the fuel and the air to form a high temperature gas stream, and a turbine that is driven by the high temperature gas stream. Other components also may be used herein. The power of the gas turbine engine is related generally to the temperature of the gas flow at various locations therethrough. Specifically, the temperature at the compressor inlet, the compression ratio, and the temperature of the combustor outlet are closely monitored during operation of the engine. Lowering the temperature of the gas flow entering the compressor generally results in increasing the output of the engine.
Known methods of reducing the temperature include the use of a power augmentation system. A power augmentation system may include a chiller coil and evaporator coolers so as to reduce the temperature of the gas stream. Known power augmentation systems are shown in, for example, U.S. Pat. No. 7,007,484 B2 and U.S. Patent Publication No. 2005/0056023 A1.
The use of a power augmentation system, however, adds resistance to the airflow entering the compressor. This resistance is defined as a pressure drop in the inlet system and may be measured in inches of water column. Turbine efficiency and power output are a direct function of the inlet system pressure drop. The higher the inlet system pressure drop, the lower the efficiency and power output of the turbine.
The power augmentation system increases the gas turbine output and efficiency when operating at the desired ambient conditions. When the power augmentation system is not operating, however, the additional pressure drop that the system adds in the air inlet stream reduces the gas turbine efficiency and output. Typical pressure drop values across the gas turbine inlet system for power generation varies from about two (2) to about five (5) inches of water column (about five (5) to about 12.7 centimeters of water). This includes the pressure drop across the power augmentation system, which varies from about 0.5 inches to about 1.5 inches of water column (about 1.27 to about 3.8 centimeters of water). Depending on the size of the gas turbine frame, the value of this pressure drop affects the gas turbine output anywhere in the range of about one (1) to about five (5) megawatts at rated ISO conditions. This in turn may affect the turbine efficiency in the range of about 0.01% to about 0.3%. Every point of efficiency and power, however, is essential in the competitive business of power generation or the variety of other uses for mechanical drive gas turbines.
There is a desire, therefore, for an air bypass system for a gas turbine inlet that reduces the pressure drop therethrough while the power augmentation systems are not operating. Such an air bypass system should increase the overall efficiency and power of the gas turbine engine.